Image-capturing system capable of reducing an amount of data related to image acquisition

ABSTRACT

To provide an image-capturing system capable of maintaining high analysis accuracy while reducing the amount of data related to image acquisition with a simple method. In order to achieve the object, the image-capturing system includes an image-capturing device configured to acquire image data of a subject, and an image-capturing control device configured to control image acquisition by the image-capturing device. The image-capturing control device includes a difference extraction means configured to extract difference data on the basis of any two image data items acquired by the image-capturing device, a change amount extraction means configured to extract change amount data on the basis of any two difference data items extracted by the difference extraction means, and a condition change means configured to change an image acquisition condition in the image-capturing device on the basis of the change amount data extracted by the change amount extraction means.

CROSS REFERENCE TO PRIOR APPLICATION

This application is a National Stage Patent Application of PCTInternational Patent Application No. PCT/JP2019/032661 (filed on Aug.21, 2019) under 35 U.S.C. § 371, which claims priority to JapanesePatent Application No. 2018-156408 (filed on Aug. 23, 2018), which areall hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an image-capturing system that acquiresan image.

BACKGROUND ART

Surveillance cameras have been conventionally used as means formonitoring any areas. Typically, image data acquired by animage-capturing device, such as a surveillance camera, is transmitted toa control center or the like via communication means. An image capturedby a surveillance camera of late has a large number of pixels and highresolution, and thus has a problem of low communication speed due to anincrease in the amount of data. Thus, in order to transmit and receiveimage data while maintaining high communication speed, it is necessaryto acquire image data while giving priority to a case where an object tobe monitored has moved.

A conventional method for detecting the movement of an object to bemonitored acquires an image every time a certain period elapses, andextracts desired data from the image to detect the movement. In thiscase, detection of the movement of the object to be monitored using onlya change at a monitoring point may erroneously determine that there is achange in spite of the fact that there is actually no change in theobject to be monitored due to a change in the solar radiation conditionor the presence or absence of illumination. Thus, in order to prevent areduction in the accuracy of the movement detection caused by theerroneous determination, for example, a movement detection devicedescribed in Patent Literature 1 has been developed.

In the movement detection device of Patent Literature 1, a monitoringscreen is provided with a first monitoring point where the movement ofan object to be monitored is detected, and a second monitoring pointwhich is not affected by the movement of the object to be monitored.When there is a change at the first monitoring point and there is nochange at the second monitoring point, it is determined that there is achange in the object to be monitored.

CITATION LIST Patent Literature

Patent Literature 1: JP H11-234652 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In the movement detection device disclosed in Patent Literature 1, thetwo monitoring points are set, and the movement detection is performedin such a manner that a change at any one of the two monitoring pointsis detected as a change in the object to be monitored except anenvironmental change. Thus, it is necessary to set monitoring pointsaccording to the installation place of a camera, which results in aproblem of a complicated operation.

Further, even when a change at one of the two monitoring point is aslight change that falls within the margin of error, the object to bemonitored is determined to have changed. Thus, the reliability isreduced, and an analysis with high accuracy cannot be performed.

As can be understood from the above description, it is an object of thepresent invention to provide an image-capturing system capable ofmaintaining high analysis accuracy while reducing the amount of datarelated to image acquisition with a simple method.

Solutions to Problems

Thus, as a result of earnest studies, the inventors of the presentinvention have conceived the following invention to solve the aboveproblems.

Specifically, an image-capturing system according to the presentinvention includes an image-capturing device configured to acquire imagedata of a subject, and an image-capturing control device configured tocontrol image acquisition by the image-capturing device. Theimage-capturing control device includes a difference extraction meansconfigured to extract difference data on the basis of any two image dataitems acquired by the image-capturing device, a change amount extractionmeans configured to extract change amount data on the basis of any twodifference data items extracted by the difference extraction means, anda condition change means configured to change an image acquisitioncondition in the image-capturing device on the basis of the changeamount data extracted by the change amount extraction means.

Effects of the Invention

The image-capturing system according to the present invention is capableof acquiring an image that enables high analysis accuracy to bemaintained while reducing the amount of data related to the imageacquisition with a simple method.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating the schematic configuration of animage-capturing system according to the present invention.

FIG. 2 is an image diagram relating to extraction of difference data andchange amount data.

FIG. 3 is an image diagram relating to extraction of local differencedata.

FIG. 4 is an image diagram relating to extraction of difference data andchange amount data.

FIG. 5 is a diagram illustrating an image of adjustment of distortionderived from a lens.

FIG. 6 is a flowchart of an image acquisition condition change process.

FIG. 7 is a flowchart of an image acquisition condition determinationprocess.

FIG. 8 is a lens sectional view of an example of an image-capturingdevice in the present invention.

FIG. 9 is a spherical aberration diagram, an astigmatism diagram, and adistortion aberration diagram of an imaging lens of the example.

DESCRIPTION OF EMBODIMENTS

Hereinbelow, an embodiment of an image-capturing system according to thepresent application will be described. Note that the image-capturingsystem described below is one aspect of the present application, and thepresent invention is not limited to the aspect described below.

As illustrated in FIG. 1, an image-capturing system 1 according to thepresent application includes an image-capturing device 2, which acquiresimage data of a subject, an image-capturing control device 3, whichcontrols image acquisition by the image-capturing device 2, and astorage unit 4, which stores the image data acquired by theimage-capturing device 2. The present application is characterized inthat the image-capturing control device 3 includes a differenceextraction unit 32, which extracts difference data on the basis of anytwo image data items acquired by the image-capturing device 2, a changeamount extraction unit 33, which extracts change amount data on thebasis of any two difference data items extracted by the differenceextraction unit 32, and a condition change unit 35, which changes animage acquisition condition in the image-capturing device 2 on the basisof the change amount data extracted by the change amount extraction unit33.

The image-capturing system 1 according to the present applicationchanges the next image acquisition condition in the image-capturingdevice 2 on the basis of change amount data which has been extracted onthe basis of two difference data items. Accordingly, the image-capturingsystem 1 is capable of determining a change in a moving object presentin a subject area of the image-capturing device 2 with high accuracy,thereby acquiring an image with high analysis accuracy maintained whilereducing the amount of data related to the image acquisition. Thepresent application is characterized particularly in the image-capturingcontrol device 3. Thus, in the following description, theimage-capturing control device 3 is described first, and theimage-capturing device 2 is then described.

1. Image-Capturing Control Device

As illustrated in FIG. 1, the image-capturing control device 3 includesan image data acquisition unit (image data acquisition means) 31, thedifference extraction unit (difference extraction means) 32, the changeamount extraction unit (change amount extraction means) 33, a datacorrection unit (data correction means) 34, the condition change unit(condition change means) 35, and an image-capturing control unit(image-capturing control means) 36. The image-capturing control device 3is, for example, provided with a CPU, and capable of implementing eachfunction by executing a predetermined program. Further, theimage-capturing control device 3 is communicably connected to theimage-capturing device 2 and the storage unit 4 via predeterminedcommunication means (not illustrated). The communication means employedherein is not particularly limited to any communication means, and maybe wired or wireless communication means. Hereinbelow, each unit will bedescribed.

1-1. Image Data Acquisition Unit

The image data acquisition unit 31 acquires image data transmitted fromthe image-capturing device 2 as needed. The image data acquisition unit31 transmits the acquired image data to the storage unit 4 as needed.Thus, image data transmitted from the image data acquisition unit 31 aresequentially stored in the storage unit 4.

1-2. Difference Extraction Unit

The difference extraction unit 32 extracts difference data on the basisof any two image data items acquired by the image-capturing device 2.Specifically, the difference extraction unit 32 extracts any two imagedata items from a plurality of image data items which have beensequentially stored in the storage unit 4 from the image dataacquisition unit 31. The difference extraction unit 32 extracts one ofthe two image data items that is captured before the other one as firstimage data and the other image data item that is captured after thefirst image data as second image data. The first image data and thesecond image data are preferable, but not particularly limited to, imagedata items that are consecutively captured (acquired). In other words,the second image data is not necessarily image data that is acquiredimmediately after the first image data, and it is only required that thesecond image data be acquired after the first image data.

The difference extraction unit 32 performs a comparison between theextracted first image data and the extracted second image data toextract difference data. The difference data is data indicating thedifference between the two compared image data items, and a data formatthereof is not particularly limited to any format. For example, asillustrated in FIG. 2, the difference extraction unit 32 performs acomparison between first image data I1 and second image data I2, andperforms arithmetic processing for extracting only a changed pixel toacquire difference data S1. At this time, the difference extraction unit32 preferably performs the extraction of the difference data on thebasis of at least either the number of pixels or the ratio of pixelsdifferent between the two image data items. Specifically, when, betweenthe first image data I1 and the second image data I2, a changed pixel isdefined as 1 and an unchanged pixel is defined as 0 to calculate thedifference data S1, it is possible to determine whether movement withinthe image is large on the basis of the number of pixels with a flagof 1. At this time, the magnitude of movement within the image may bedetermined on the basis of the ratio of the number of changed pixels tothe number of pixels in the entire image. In a case where theimage-capturing device 2 is a fixed-point camera which is installed in afixed manner at a predetermined position, a change in the entire imageis often small, and the calculation of the image change using differencedata as performed in the present invention is thus particularlyeffective in reducing the amount of data.

Further, as illustrated in FIG. 3, the difference extraction unit 32preferably divides the whole of each of the two extracted image dataitems into a plurality of blocks (hereinbelow, also referred to as“local blocks”), and extracts local difference data for each of thelocal blocks. In the extraction of the local difference data, thedifference extraction unit 32 divides the whole of each of the twoextracted image data items into local blocks, and compares specificlocal blocks having corresponding positional information in the twoimage data items to extract the local difference data. The specificlocal block can be set in any manner, and the number of specific localblocks may be one or more. When the difference data extracted by thedifference extraction unit 32 is the local difference data extracted foreach local block in this manner, it is possible to estimate a movingdirection and a moving speed of a moving object with high accuracy andmore precisely change the “image acquisition condition in theimage-capturing device”, which will be described below.

The difference data or the local difference data extracted by thedifference extraction unit 32 described above are sequentiallytransmitted to the storage unit 4 and stored in the storage unit 4. Atthis time, the image data stored in the storage unit 4 preferablyincludes information of a time when the image is captured because of thefollowing reason. When each of any two image data items extracted by thedifference extraction unit 32 includes information of a time when theimage is captured, the difference extraction unit 32 can perform acomparison between the information of the time when the first image datais captured and the information of the time when the second image datais captured to calculate an acquisition interval between the time pointwhen the first image data is captured and the time point when the secondimage data is captured. Although an example in which the image dataincludes the information of the time when the image is captured isdescribed herein, alternatively, the acquisition interval between thefirst image data and the second image data may be calculated frominformation related to a frame rate when the image is captured. When theacquisition interval between the first image data and the second imagedata can be calculated at the time of extracting the difference data, itis possible to change the “image acquisition condition in theimage-capturing device”, which will be described in detail below, withhigh accuracy.

1-3. Change Amount Extraction Unit

The change amount extraction unit 33 extracts change amount data on thebasis of any two difference data items extracted by the differenceextraction unit 32, and sequentially transmits the extracted changeamount data to the storage unit 4 to store the change amount data in thestorage unit 4. Specifically, the change amount extraction unit 33extracts any two difference data items from a plurality of differencedata items which have been sequentially stored in the storage unit 4from the difference extraction unit 32. The change amount extractionunit 33 extracts one of the two difference data items that is extractedfrom image data captured before the other image data as first differencedata and the other difference data that is extracted from image datacaptured after the image data used in the extraction of the firstdifference data as second difference data. The first difference data andthe second difference data are preferably, but not particularly limitedto, difference data items extracted from the image data items that areconsecutively captured (acquired). In other words, the second differencedata is not necessarily difference data that is extracted using imagedata acquired immediately after the image data used in the extraction ofthe first difference data, and it is only required that the seconddifference data be difference data that is extracted using image dataacquired after the first image data. However, it is preferable toextract the change amount data using difference data items that areextracted from image data items consecutively captured because anoptimum image acquisition condition can be set.

The change amount extraction unit 33 performs a comparison between theextracted first difference data and the extracted second difference datato extract change amount data. The change amount data is data indicatingthe difference (change amount) between the two compared difference dataitems, that is, a change amount of any one of the difference data itemswith respect to the other difference data item, and a data formatthereof is not particularly limited to any format. Specifically, thechange amount extraction unit 33 performs a comparison between the firstdifference data S1 and the second difference data S2, and performsarithmetic processing for extracting only a changed pixel to acquirechange amount data H1. At this time, the change amount extraction unit33 preferably performs the extraction of the change amount data on thebasis of at least either the number of pixels or the ratio of pixelsdifferent between the two difference data items as with the differenceextraction unit 32.

For example, the change amount data H1 illustrated in FIG. 2 is acquiredfrom the first difference data S1 and the second difference data S2which are extracted on the basis of image data I1, image data I2, andimage data I3 obtained by consecutively capturing a state in which aperson moves within the subject area of the image-capturing device 2 ata predetermined frame rate. As illustrated in FIG. 2, the differencebetween the first difference data S1 and the second difference data S2is only person image data of the image data I1 and person image data ofthe image data I3, and the number of changed pixels is hardly changedcompared to the first difference data S1 and the second difference dataS2. Thus, the change amount data H1 extracted by the change amountextraction unit 33 in the case of FIG. 2 has a small value.

On the other hand, change amount data H2 illustrated in FIG. 4 isacquired from first difference data S3 and second difference data S4which are extracted on the basis of image data 14, image data 15, andimage data I6 obtained by consecutively capturing, in addition to astate in which a person moves within the subject area of theimage-capturing device 2, a state in which another person enters thesubject area at a predetermined frame rate. As illustrated in FIG. 4,the difference between the first difference data S3 and the seconddifference data S4 is person image data that first appears in the imagedata I6 in addition to person image data of the image data 14 and personimage data of the image data I6, and the number of changed pixels isincreased compared to the first difference data S3 and the seconddifference data S4. Thus, the change amount data H2 of FIG. 4 has alarger change amount than the change amount data H1 of FIG. 2.

As illustrated in FIG. 2, even when the data amount of the firstdifference data S1 and the second difference data S2 is large, the dataamount of the change amount data H1, which is the difference between thefirst difference data S1 and the second difference data S2, may not bedifferent from that of the difference data. In this case, even when amoving object is present in the subject area of the image-capturingdevice 2, it can be determined that there is no change in the movingspeed and the amount of the moving object. In this case, it is possibleto maintain the current image acquisition condition without changing theimage acquisition condition in the image-capturing device 2.

On the other hand, as illustrated in FIG. 4, when the data amount of thefirst difference data S3 and the second difference data S4 is large, andthe data amount of the change amount data H2, which is the differencebetween the first difference data S3 and the second difference data S4,becomes larger than that of the difference data, it can be determinedthat a moving object is present in the subject area of theimage-capturing device 2 and the change amount of the moving object islarge. In this case, the image acquisition condition in theimage-capturing device 2 can be changed to a condition with higheraccuracy.

Although the present embodiment describes an example in which the imageacquisition condition is changed using the data amount of the changeamount data and the data amount of the difference data, the presentapplication is not limited thereto. For example, when the change amountdata H2 illustrated in FIG. 4 is extracted after the change amount dataH1 illustrated in FIG. 2, since the data amount of the change amountdata H2 is larger than the data amount of the change amount data H1, itcan be determined that the change amount of the moving object is large.In this case, the image acquisition condition in the image-capturingdevice 2 may be changed to a condition with higher accuracy. In thismanner, two change amount data items can also be used in the imageacquisition condition change process.

Further, the change amount extraction unit 33 preferably extracts thechange amount data on the basis of the local difference data describedabove. When the change amount data is extracted on the basis of thelocal difference data, the change amount extraction unit 33 extracts anytwo local difference data items having the corresponding positionalinformation in the image data items from the storage unit 4. Forexample, FIG. 3 illustrates an image in which the whole image of each ofthe first difference data S1 and the second difference data S2 isdivided into a plurality of local blocks. In FIG. 3, two localdifference data items having the corresponding positional information atany positions in the first difference data S1 and the second differencedata S2 are highlighted with a thick line. When focusing on thehighlighted local difference data items in FIG. 3, it can be understoodthat the data amount of the local difference data of the seconddifference data S2, which is extracted after the first difference dataS1, is larger than the data amount of the local difference data of thefirst difference data S1. In other words, the change amount of thesecond local difference data relative to the first local difference data(local change amount data) is large. On the other hand, for example,when the upper left local difference data items of the respectivedifference data items are compared with each other, the local changeamount is small. In this manner, it is possible to perform estimation ofthe moving direction and the moving speed of the moving object withhigher accuracy by using the local difference data. Thus, the changeamount data (local change amount data) can be extracted with highaccuracy on the basis of the local difference data, which enables moreprecise setting of the image acquisition condition. Note that details ofsetting change control of the “image acquisition condition in theimage-capturing device” based on the change amount data extracted by thechange amount extraction unit 33 will be described below.

1-4. Data Correction Unit

The image-capturing system 1 according to the present applicationpreferably includes a data correction unit 34, which performs errorcorrection on the difference data described above. The error correctionperformed by the data correction unit 34 includes a case where thedifference data is divided into local blocks, and a slight change causedby an environmental change is adjusted, and a case where distortionderived from the image-capturing device 2 is adjusted. Although thepresent embodiment describes the case where the error correction isperformed on the difference data, the present application is not limitedthereto. The present application may be applied to a case where errorcorrection is performed on the change amount data, or error correctionmay be performed on both the difference data and the change amount data.

1-4-1. Error Correction Using Local Block

Typically, in a case where the image-capturing device 2 is fixed at afixed point, image data of a subject may include a fixed object.Examples of the fixed object include a tree as illustrated in FIG. 2 anda building. The amount of light in these fixed objects may be slightlychanged when leaves of the tree sway in the wind or due to a solarradiation condition. A change in the image data caused by theenvironmental change in the fixed objects falls within the margin oferror. Thus, sensitively changing the image acquisition conditionreduces reliability and disables an analysis with high accuracy.

Thus, the data correction unit 34 may divide the whole of the differencedata into a plurality of local blocks, and correct the difference dataassuming that there is no change when the changed data amount fallswithin a predetermined error amount for each of the local blocks. Inthis case, the data correction unit 34 previously sets an error amountfor each local block. The error amount may be set as a predeterminedthreshold or a range having an upper limit and a lower limit. A preciseimage acquisition condition can be set using difference data with higheraccuracy by correcting the data amount of difference data for each localblock on the basis of the error amount.

1-4-2. Error Correction by Adjustment of Distortion Derived fromImage-capturing Device

Typically, image data of a three-dimensional image acquired by animage-capturing device using a lens having a wide angle of view has alarger distortion in the peripheral region than the central region dueto a perspective effect. Thus, the data correction unit 34 corrects thedifference data amount in the peripheral region of the image data on thebasis of the characteristics of an imaging lens 21, which is attached tothe image-capturing device 2 included in the image-capturing system 1.As an example, FIG. 5 illustrates an image of difference data havingpixels arranged in a predetermined horizontal direction beforecorrection and an image after the correction. In FIG. 5, first pixeldata and second pixel data are compared with each other, and a changedpixel is indicated as 1 and an unchanged pixel is indicated as 0. In thepixel data before the correction, pixel data items of “1111” arearranged in the image peripheral part surrounded by a square. For thesepixel data items, the data correction unit 34 assumes that the imageperipheral part has distortion based on the characteristics of theimaging lens 21, and corrects “1111” in the image peripheral part to“0110” to adjust the difference data assuming that there is no pixelchange caused by distortion.

Accordingly, it is possible to adjust the distortion in the imageperipheral part of the image according to the characteristics of theimaging lens 21 attached to the image-capturing device 2. Thus, it ispossible to set a precise image acquisition condition using differencedata with higher accuracy.

1-5. Condition Change Unit

The condition change unit 35 sets the image acquisition condition in theimage-capturing device 2 by the image-capturing control unit 36 on thebasis of the change amount data extracted by the change amountextraction unit 33. Here, the image acquisition condition is, forexample, at least one of an acquisition interval, the number of pixels,a resolution, a color tone (gray scale), and a size, of images.Specifically, the image acquisition interval indicates a period from atime point when the image-capturing device 2 acquires image data lasttime to a time point when the image-capturing device 2 acquires nextimage data.

Further, the image acquisition condition in the present invention is notlimited to a condition related to capturing of an image in theimage-capturing device 2. For example, the image acquisition conditionmay be a condition of storing an image acquired by the image-capturingdevice 2 in the storage unit 4 by the image data acquisition unit 31. Inthis case, the image acquisition condition is, for example, at least oneof a storage interval with respect to the storage unit 4 (imageacquisition interval), the number of pixels, the resolution, the colortone (gray scale), and the size, of images. As an example, the conditionchange unit 35 changes the image acquisition condition by changing thestorage interval with respect to the storage unit 4 instead of the imageacquisition interval in the image-capturing device 2. This also enablesthe condition change unit 35 to reduce the capacity of images stored inthe storage unit 4 by increasing (extending) the image storage intervalwith respect to the storage unit 4 without changing the image capturinginterval in the image-capturing device 2. Thus, it is possible to reducethe amount of data related to image acquisition with a simple method.

Data related to the image acquisition condition is previously stored inthe storage unit 4. The condition change unit 35 performs a comparisonbetween the data related to the image acquisition condition stored inthe storage unit 4, for example, threshold data and the change amountdata acquired by the change amount extraction unit 33 and changes thenext image acquisition condition in the image-capturing device 2. Asdescribed above, the next image acquisition condition can be changed onthe basis of the change amount of a moving object present in the subjectarea of the image-capturing device 2 by using the change amount dataacquired by the change amount extraction unit 33. Thus, it is possibleto obtain monitoring image data of the moving object with high accuracywhile reducing the amount of data related to image acquisition. Further,the condition change unit 35 also preferably changes the next imageacquisition condition in the image-capturing device 2 on the basis ofnot only the change amount data, but also the difference data extractedby the difference extraction unit 32 in addition to the change amountdata. Note that specific setting change control of the “imageacquisition condition in the image-capturing device” based on the changeamount data will be described below.

1-6. Image-Capturing Control Unit

The image-capturing control unit 36 controls the image-capturing device2 in accordance with the image acquisition condition input from thecondition change unit 35 described above to perform the next subjectimage data acquisition.

2. Storage Unit

The storage unit 4 includes a ROM which is a nonvolatile memory, and aRAM which is a volatile memory. The storage unit 4 is communicablyconnected to the image-capturing control device 3 described above viacommunication means to enable transmission and reception of image dataand various control signals. The communication means employed herein isnot particularly limited to any control means, and may be wired orwireless control means.

The storage unit 4 stores various data items including image datareceived from the image-capturing control device 3 via the communicationmeans. Further, the storage unit 4 stores various data items related tothe image acquisition condition which are used in the change of theimage acquisition condition by the condition change unit 35.

Note that, although the storage unit 4 is provided separately from theimage-capturing control device 3 in the present embodiment, the presentapplication is not limited thereto. The storage unit 4 may beincorporated in the image-capturing control device 3.

3. Image-Capturing Device

Next, the image-capturing device 2 will be described. Theimage-capturing device 2 in the present application includes at leastthe imaging lens (optical system) 21, which forms a subject image, andan image sensor 22, which acquires the image formed by the imaging lens21. The image sensor 22 is not particularly limited to any sensor, and asolid-state image sensor such as a CCD sensor or a CMOS sensor can alsobe used. The image-capturing device 2 in the present application issuitable for image-capturing devices using these image sensors such as adigital camera and a video camera. Further, it is needless to say thatthe image-capturing device 2 may be a lens-fixed type image-capturingdevice including a lens fixed to a housing or a lens-replaceableimage-capturing device such as a single lens reflex camera or amirrorless camera.

In the image-capturing system 1 according to the present application,the imaging lens 21 and the image sensor 22 preferably satisfyconditions described below. Hereinbelow, the conditions that the imaginglens 21 and the image sensor 22 preferably satisfy will be described.

3-1. Conditional Expression (1)

The imaging lens 21 and the image sensor 22 according to the presentapplication preferably satisfy the following Conditional Expression (1).50<f×tan ω/P  (1)where

f is the focal length of the imaging lens,

ω is the angle of view of the imaging lens, and

P is the pixel center distance between adjacent pixels

of the image sensor.

The above Conditional Expression (1) is an expression that defines theratio between the size of an image plane of the imaging lens 21 and apixel pitch. A numerical range of Conditional Expression (1) is definedbecause of the following reason. When a value of f×tan ω/P ofConditional Expression (1) is larger than 50, a change in an image canbe accurately extracted. The lower limit of Conditional Expression (1)is preferably 80, more preferably 120, even more preferably 200, evenmore preferably 400, and even more preferably 600.

Only the lower limit is defined in the above Conditional Expression (1)because it is not necessary to define the upper limit when consideredfrom the viewpoint of those skilled in the art. However, if the upperlimit is defined, the upper limit is preferably 8000, more preferably4000, and even more preferably 2500 in view of the data amount and cost.

3-2. Conditional Expression (2)

The imaging lens 21 according to the present application preferablyincludes at least one lens L and satisfies the following ConditionalExpression (2).1.48<NdL<2.30  (2)

where

NdL is the refractive index of the lens included in the imaging lens atthe d-line.

The above Conditional Expression (2) is an expression that defines therefractive index of the lens L included in the imaging lens 21. When avalue of NdL in Conditional Expression (2) satisfies the above numericalrange, cost of the imaging lens can be reduced. The upper limit ofConditional Expression (2) is more preferably 2.10, even more preferably1.95, even more preferably 1.89, even more preferably 1.84, even morepreferably 1.78, even more preferably 1.68, and even more preferably1.60.

Further, the lens L included in the imaging lens 21 preferably has thelowest refractive index among lenses included in the imaging lens 21 inview of correcting the Petzval sum.

3-3. Conditional Expression (3)

All lenses included in the imaging lens 21 according to the presentapplication preferably satisfy the following Conditional Expression (3).1.48<Nd<2.30  (3)

where

Nd is the refractive index of the lens at the d-line.

The above Conditional Expression (3) is an expression that defines therefractive index of all the lenses included in the imaging lens 21. Whena value of Nd in Conditional Expression (3) satisfies the abovenumerical range, cost of the imaging lens can be reduced. The upperlimit of Conditional Expression (3) is more preferably 2.10, even morepreferably 1.95, even more preferably 1.89, even more preferably 1.84,even more preferably 1.78, even more preferably 1.68, and even morepreferably 1.60.

4. Process in Image-Capturing System

With the above configuration, the image-capturing control device 3acquires image data from the image-capturing device 2, performs theextraction of difference data and the extraction of change amount data,and changes the image acquisition condition in the image-capturingdevice 2 as needed. Hereinbelow, the image acquisition condition changeprocess of the image-capturing system 1 according to the presentapplication will be described with reference to a flowchart of FIG. 6.

4-1. Image Acquisition Condition Change Process

First, the image data acquisition unit 31 acquires image data from theimage-capturing device 2, and transmits the acquired image data to thestorage unit 4 as needed to store the image data in the storage unit 4.Note that, at an early stage when the image acquisition condition changeprocess has not yet been performed, the image data is acquired on imageacquisition conditions that the frame rate is 15 fps and the image sizeis 2 MB as an early-stage image acquisition condition in theimage-capturing device 2.

Next, the difference extraction unit 32 extracts any two image dataitems from the storage unit 4 (Step 1), and performs a difference dataextraction process (Step 2). Specifically, the difference extractionunit 32 reads two image data items acquired at different timings,specifically, the first image data and the second image data from thestorage unit 4, and performs a comparison between the first image dataand the second image data to extract difference data. The extracteddifference data is transmitted to the condition change unit 35, and alsotransmitted to the storage unit 4 and stored in the storage unit 4.

Here, the second image data acquired after the first image data ispreferably most recently acquired image data in order to appropriatelyset the next image acquisition condition. Further, the difference datais preferably stored associated with time information of the first imagedata and time information of the second image data, the first image dataand the second image data being used in the extraction of the differencedata. At this time, the difference extraction unit 32 may calculate anacquisition interval (capturing interval between the time point when thefirst image data is captured and the time point when the second imagedata is captured) from the time information of the first image data andthe time information of the second image data, and store the differencedata associated with the information related to the acquisitioninterval.

Then, the change amount extraction unit 33 extracts any two differencedata items from the storage unit 4, and performs a change amount dataextraction process (Step 3). Specifically, the change amount extractionunit 33 reads two different difference data items, specifically, thefirst difference data and the second difference data from the storageunit 4, and performs a comparison between the first difference data andthe second difference data to extract change amount data. The extractedchange amount data is transmitted to the condition change unit 35, andalso transmitted to the storage unit 4 and stored in the storage unit 4.

Here, the difference data extracted from the storage unit 4 by thechange amount extraction unit 33 is preferably difference data on whicherror correction has been performed by the data correction unit 34described above because of the following reason. It is possible toeliminate information based on an error in advance and extract thechange amount data with high accuracy by using the previouslyerror-corrected data as the difference data used in the extraction ofthe change amount data.

Next, the condition change unit 35 executes an image acquisitiondetermination process on the basis of the difference data input from thedifference extraction unit 32 and the change amount data input from thechange amount extraction unit 33 (Step 4). Note that details of theimage acquisition determination process will be described below withreference to another drawing.

After determining the next image acquisition condition in the imageacquisition condition determination process, the condition change unit35 then updates the image acquisition condition stored in the storageunit 4 to the new image acquisition condition (Step 5). Then, thecondition change unit 35 transmits the new image acquisition conditionto the image-capturing device 2. The image-capturing device 2 acquiresthe next image data in accordance with the new image acquisitioncondition.

4-2. Image Acquisition Condition Determination Process

Next, the image acquisition condition determination process will bedescribed with reference to FIG. 7.

First, the condition change unit 35 acquires difference data from thedifference extraction unit 32 and change amount data from the changeamount extraction unit 33 (Step 10). Then, the condition change unit 35acquires data related to the image acquisition condition from thestorage unit 4 (Step 11). Concrete examples of the data related to theimage acquisition condition include a change amount threshold and adifference threshold for each of the acquisition interval, the number ofpixels, the resolution, the color tone (gray scale), and the size, ofimages. Further, the storage unit 4 stores a minimum value and/or amaximum value as setting for each image acquisition condition, and thecondition change unit 35 also reads information related to the minimumvalue and the maximum value together with the change amount thresholdand the difference threshold from the storage unit 4.

Then, the condition change unit 35 determines whether the data amount ofthe acquired change amount data is currently equal to or larger than thechange amount threshold read from the storage unit 4 (Step 12). When thecondition change unit 35 has determined that the data amount of thechange amount data is equal to or larger than the change amountthreshold (Yes in Step 12), the condition change unit 35 changes thenext image acquisition condition so as to make the image data amountlarger than the image data amount under the current image acquisitioncondition (Step 13). The data amount of the change amount data equal toor larger than the change amount threshold means that the number ofchanged pixels calculated from the two difference data items is large,that is, the change amount of the moving object present in the subjectarea of the image-capturing device 2 is large. Thus, in order to capturethe state of the change in the moving object with higher accuracy, thecondition change unit 35 changes the image acquisition condition so asto increase the image data amount. Specifically, in the case where theimage acquisition condition is the image acquisition interval, theacquisition interval is shortened. In the case where the imageacquisition condition is the frame rate, the frame rate is increased.Further, in the case where the image acquisition condition is the numberof pixels, the resolution, the color tone, or the image size of an imageto be captured, the number of pixels, the resolution, the color tone, orthe image size is increased. In the present application, the imageacquisition condition is not limited to one condition, and theseconditions may be combined to set the image acquisition condition.

On the other hand, when the condition change unit 35 has determined thatthe data amount of the acquired change amount data is currently smallerthan the change amount threshold read from the storage unit 4 in Step 12(No in Step 12), the condition change unit 35 proceeds to Step 14 todetermine whether the difference data is equal to or larger than thedifference threshold. In the present application, based on only the dataamount of the change amount data, when the data amount of the changeamount data is smaller than the change amount threshold, the currentimage acquisition condition may be maintained, or the image acquisitioncondition may be changed so as to reduce the image data amount. However,in order to change the setting of the image acquisition condition withhigher accuracy, in the present embodiment, the condition change unit 35determines whether the data amount of the acquired difference data isequal to or larger than the difference threshold read from the storageunit 4 in Step 14.

The determination that the data amount of the difference data is equalto or larger than the difference threshold (Yes in Step 14) means thatthe number of changed pixels calculated from the two difference dataitems is large, that is, the change amount of the moving object presentin the subject area of the image-capturing device 2 is a certain degreeor more. Thus, when the condition change unit 35 has determined that thedata amount of the change amount data is smaller than the change amountthreshold, but the data amount of the difference data is equal to orlarger than the difference threshold, the condition change unit 35preferably maintains the current image acquisition condition withoutimmediately changing the image acquisition condition so as to reduce theimage data amount (Step 15). In this manner, the current imageacquisition condition can be maintained taking into consideration notonly the data amount of the change amount data, but also thedetermination that the data amount of the difference data is equal to orlarger than the predetermined threshold. Thus, it is possible to achieveimage acquisition with higher accuracy taking into consideration thestate of the change in the moving object present in the subject area.

On the other hand, when the condition change unit 35 has determined thatthe data amount of the difference data is smaller than the differencethreshold in Step 14 (No in Step 14), since not only the data amount ofthe change amount data, but also the data amount of the difference datais smaller than the predetermined threshold, the condition change unit35 changes the next image acquisition condition so as to reduce theimage data amount (Step 16). The data amount of the difference datasmaller than the difference threshold means that the number of changedpixels calculated from the two image data items is small or almost zero,that is, the change amount of the moving object present in the subjectarea of the image-capturing device 2 is small or almost zero. Thus,specifically, in the case where the image acquisition condition is theacquisition interval, the condition change unit 35 extends theacquisition interval. In the case where the image acquisition conditionis the frame rate, the condition change unit 35 reduces the frame rate.Further, in the case where the image acquisition condition is the numberof pixels, the resolution, the color tone, or the image size of an imageto be captured, the number of pixels, the resolution, the color tone, orthe image size is reduced. In the present application, the imageacquisition condition is not limited to one condition, and theseconditions may be combined to set the image acquisition condition.

When the state in which the change amount data and the difference dataare equal to or larger than the respective thresholds is continued byrepeatedly executing the image acquisition condition change processdescribed above, the condition change unit 35 preferably determineswhether the changed image acquisition condition is equal to or smallerthan a predetermined maximum value (the upper limit of the image dataamount) stored in the storage unit 4, and sets the changed imageacquisition condition to the maximum value when the changed imageacquisition condition is larger than the maximum value. Accordingly, itis possible to prevent an excessive load from being applied to theimage-capturing system due to the image data becoming huge more thannecessary.

Further, when the state in which the change amount data and thedifference data are smaller than the respective thresholds is continued,the condition change unit 35 preferably determines whether the changedimage acquisition condition is equal to or larger than a predeterminedminimum value (the lower limit of the image data amount) stored in thestorage unit 4, and sets the changed image acquisition condition to theminimum value when the changed image acquisition condition is lower thanthe minimum value. Accordingly, it is possible to prevent the accuracyof the image data from being reduced more than necessary.

Next, the image-capturing device 2 in the present application will bespecifically described with an example. However, the present applicationis not limited to the example described below. In the lens sectionalview illustrated in the following example, the left side in the drawingcorresponds to an object side, and the right side in the drawingcorresponds to an image side.

EXAMPLES

(1) Configuration of Imaging Lens

FIG. 8 illustrates an imaging lens 21 of the example of theimage-capturing device 2 in the present application. As illustrated inFIG. 8, the imaging lens 21 includes a first lens G1 which has negativerefractive power and has a convex image-side surface, a second lens G2which has negative refractive power and has a meniscus shape convextoward the image side, a third lens G3 which has positive refractivepower and has a biconvex shape, a fourth lens G4 which has positiverefractive power and has a biconvex shape, a fifth lens G5 which haspositive refractive power and has a biconvex shape, a sixth lens G6which has negative refractive power and has a biconcave shape, and aseventh lens G7 which has positive refractive power and has a biconvexshape, in this order from the object side. Further, the fifth lens G5and the sixth lens G6 in this example constitute a cemented lens.

In this example, an optical block G is disposed between the seventh lensG7 and an image plane IP. The optical block G corresponds to an opticalfilter, a crystal low-pass filter, an infrared cut filter, or the like.

In the case where the image-capturing device 2 includes the imaging lens21 of the example, the image plane IP corresponds to an image-capturingsurface of a solid-state image sensor. A photoelectric conversionelement such as the CCD sensor or the CMOS sensor described above can beused as the solid-state image sensor. In the image-capturing device 2,light incident from the object side of the imaging lens 21 of thepresent embodiment is finally focused on the image-capturing surface ofthe solid-state image sensor. Then, the solid-state image sensorphotoelectrically converts the received light, and outputs thephotoelectrically-converted light as an electric signal to generate adigital image corresponding to an image of the subject. The digitalimage is transmitted as image data to the image data acquisition unit 31of the image-capturing control device 3.

(2) Numerical Example

Next, a numerical example to which specific numerical values of theimaging lens 21 are applied will be described. Surface data of theimaging lens will be shown below. In the surface data, “surface number”denotes the order of the lens surface from the object side, “r” denotesthe curvature radius of the lens surface, “d” denotes the distancebetween lens surfaces on the optical axis, “nd” denotes the refractiveindex at the d-line (wavelength λ=587.56 nm), and “νd” denotes the Abbenumber at the d-line. Further, “ASPH” next to the surface numberindicates that the lens surface is an aspherical surface. Note that alllengths in the following table are in “mm”. Further, “INF” in the fieldof the curvature radius indicates a plane.

Surface number r d nd νd  1 −300.14 1.00 1.773 49.6  2 6.31 3.91  3−8.89 5.00 1.806 33.3  4 −19.31 1.88  5ASPH 24.79 5.00 1.851 40.1  6ASPH−24.58 4.52  7ASPH 10.91 3.25 1.497 81.6  8ASPH −11.66 0.20  9 22.952.69 1.593 68.6 10 −9.98 0.70 1.728 28.3 11 8.45 3.36 12ASPH 9.01 5.001.497 81.6 13ASPH −55.95 2.49 14 INF 0.30 1.517 64.2 15 INF 0.50 Imageplane INF

Various pieces of data of the imaging lens 21 will be shown below.Specifically, the focal length (mm), the F number, the half angle ofview (w/°), the image height (mm), and the lens total length (mm) of theimaging lens are shown. Here, the lens total length is the distancebetween the object-side surface of the first lens and the image plane.

Focal length (mm) 4.93 F number (F number) 1.59 Half angle of view (°)60.00 Image height (mm) 4.22 Lens total length (mm) 40.79

An aspherical coefficient in a case where the shape of the aboveaspherical surface (ASPH) is defined by the following formula will beshown below. Note that the aspherical coefficient can be represented bythe following aspherical formula with a displacement in the optical-axisdirection at the position of the height h from the optical axis as areference surface vertex. Further, in the following, “E-a” means“X10-a”.

Surface number (1 + k) A4 A6 A8 A10 5 1.000 −4.731E−05 5.182E−07 1.476E−08  3.046E−11 6 1.000  1.980E−05 1.778E−06  1.047E−09  4.342E−107 1.000 −2.665E−04 3.086E−07 −5.887E−09 −1.470E−10 8 1.000  7.763E−056.302E−07 −1.375E−08 −4.614E−12 12 1.000 −3.050E−04 −4.460E−06  7.105E−08 −7.762E−09 13 1.000 −5.956E−04 −3.872E−06  −2.607E−08−1.873E−09Z=ch ²/[1+{1−(1+k)c ² h ²}^(1/2)]+A4h ⁴ +A6h ⁶ +A8h ⁸ +A10h ¹⁰

where c denotes the curvature (1/r), h denotes the height from theoptical axis, k denotes the conic constant, and A4, A6, A8 and A10 areaspherical coefficients of the respective orders.

In the image-capturing device 2, the number of pixels of the usedsolid-state image sensor is 2 million pixels. In this case, a value of Pis 0.004 mm, and a value of Conditional Expression (1) is 2135. Further,the number of pixels of the used solid-state image sensor may be 0.5million pixels. In this case, a value of P is 0.008 mm, and a value ofConditional Expression (1) is 1068.

FIG. 9 is a longitudinal aberration diagram when the imaging lens 21 ofthe present example is focused on infinity. The longitudinal aberrationdiagram of FIG. 9 illustrates spherical aberration (SA/mm), astigmatism(AST/mm), and distortion aberration (DIS/%) in this order from the leftin the drawing.

The vertical axis of the spherical aberration diagram represents the Fnumber. The spherical aberration diagram illustrates sphericalaberration at the d-line (wavelength: 587.56 nm), spherical aberrationat the C-line (wavelength: 656.27 nm), and spherical aberration at theg-line (wavelength: 435.84 nm).

The vertical axis of the astigmatism diagram represents the image height(Y). Further, the astigmatism diagram illustrates astigmatisms of asagittal ray S (solid line) and a meridional ray T (broken line) at thed-line (wavelength: 587.56 nm).

The vertical axis of the distortion aberration diagram represents theimage height (Y). Further, distortion aberration (distortion) at thed-line (wavelength: 587.56 nm) is indicated by a solid line.

INDUSTRIAL APPLICABILITY

The image-capturing system according to the present invention is capableof acquiring an image that enables high analysis accuracy to bemaintained while reducing the amount of data related to the acquisitionof the image. Thus, observation with higher accuracy can be performed byemploying the image-capturing system, for example, in a fixed-pointcamera or a surveillance camera. In addition to the above, an analysisrelated to a moving object can be performed with high accuracy on thebasis of the difference data and the change amount data. Thus, highlysophisticated estimation of the moving speed and the moving locus of themoving object can be performed by employing the image-capturing system,for example, in an onboard camera. Thus, it is possible to improve thepossibility of risk prevention.

REFERENCE SIGNS LIST

-   1 image-capturing system-   2 image-capturing device-   3 image-capturing control device-   4 storage unit-   21 imaging lens-   22 image sensor-   31 image data acquisition unit (image data acquisition means)-   32 difference extraction unit (difference extraction means)-   33 change amount extraction unit (change amount extraction means)-   34 data correction unit (data correction means)-   35 condition change unit (condition change means)-   36 image-capturing control unit (image-capturing control means)

The invention claimed is:
 1. An image-capturing system comprising: animage-capturing device configured to acquire image data of a subject;and an image-capturing control device configured to control imageacquisition by the image-capturing device, the image-capturing controldevice including a difference extraction unit configured to extractdifference data on the basis of any two image data items acquired by theimage-capturing device, a change amount extraction unit configured toextract change amount data on the basis of any two difference data itemsextracted by the difference extraction unit, and a condition change unitconfigured to change an image acquisition condition in theimage-capturing device on the basis of the change amount data extractedby the change amount extraction unit, wherein the difference extractionunit, the change amount extraction unit, and the condition change unitare each implemented via at least one processor.
 2. The image-capturingsystem according to claim 1, wherein the image acquisition condition isat least one of an acquisition interval, a number of pixels, aresolution, a color tone, or a size, of images.
 3. The image-capturingsystem according to claim 1, wherein when an amount of the change amountdata is equal to or larger than a predetermined change amount threshold,the condition change unit is further configured to change the imageacquisition condition so as to make an image data amount larger than animage data amount under a current image acquisition condition.
 4. Theimage-capturing system according to claim 1, wherein when an amount ofthe change amount data is smaller than a predetermined change amountthreshold, the condition change unit is further configured to maintainthe image acquisition condition or change the image acquisitioncondition so as to make an image data amount smaller than an image dataamount under a current image acquisition condition.
 5. Theimage-capturing system according to claim 4, wherein when an amount of anewest one of the two difference data items is equal to or larger than apredetermined difference threshold, the condition change unit is furtherconfigured to maintain the current image acquisition condition.
 6. Theimage-capturing system according to claim 4, wherein when an amount of anewest one of the two difference data items is smaller than apredetermined difference threshold, the condition change unit is furtherconfigured to change the image acquisition condition so as to make animage data amount smaller than an image data amount under the currentimage acquisition condition.
 7. The image-capturing system according toclaim 1, wherein the condition change unit is further configured to seta minimum value and/or a maximum value of the image acquisitioncondition.
 8. The image-capturing system according to claim 1, whereinthe difference extraction unit is further configured to extract thedifference data on the basis of at least either the number of pixels ora ratio of pixels different between the two image data items.
 9. Theimage-capturing system according to claim 1, wherein the change amountextraction unit is further configured to extract the change amount dataon the basis of at least either the number of pixels or a ratio ofpixels different between the two difference data items.
 10. Theimage-capturing system according to claim 1, wherein the imageacquisition condition is an image acquisition interval, and thedifference extraction unit is further configured to calculate the imageacquisition interval on the basis of an acquisition interval between thetwo image data items.
 11. The image-capturing system according to claim1, wherein the difference extraction unit is further configured todivide a whole of each of the two image data items into a plurality oflocal blocks, and extract local difference data for each of the localblocks to extract the difference data.
 12. The image-capturing systemaccording to claim 11, wherein the change amount extraction unit isfurther configured to extract the change amount data on the basis of thelocal difference data.
 13. The image-capturing system according to claim1, further comprising a data correction unit configured to adjust errordata included in the difference data and/or the change amount data,wherein the data correction unit is implemented via at least oneprocessor.
 14. The image-capturing system according to claim 13, whereinthe data correction unit is further configured to divide a whole of eachimage data acquired in the image-capturing device into a plurality oflocal blocks, and adjust the error data for each of the local blocks.15. The image-capturing system according to claim 13, wherein theimage-capturing device includes an imaging lens configured to form asubject image, and an image sensor configured to acquire the subjectimage formed by the imaging lens, and the data correction unit isfurther configured to adjust error data caused by distortion dependenton an angle of view of the imaging lens.
 16. The image-capturing systemaccording to claim 1, wherein the image-capturing device includes animaging lens configured to form a subject image, and an image sensorconfigured to acquire the subject image formed by the imaging lens, andsatisfies the following condition (1),50<f×tan ω/P  (1) where f is a focal length of the imaging lens, ω is anangle of view of the imaging lens, and P is a pixel center distancebetween adjacent pixels of the image sensor.
 17. The image-capturingsystem according to claim 1, wherein the image-capturing device is fixedat a fixed point.